As typical methods for achieving an extended depth of field (hereinafter, referred to as EDOF), three methods described below can be primarily provided. The first method is to unify a blur in a depth direction by inserting an optical device referred to as a phase plate into an optical system. In this method, image restoration processing is performed on an obtained image, using a previously-measured blur pattern or a blur pattern calculated by simulation, thereby producing an EDOF image. The method is referred to as Wavefront coding (hereinafter, “WFC”).
The second method is to perform a highly-accurate distance measurement for each of partial ranges in the image by devising a shape of an aperture. In this method, the image restoration processing is performed on each of the partial ranges, using blur patterns according to previously predicted respective distances, thereby producing the EDOF image. The method is referred to as a coded aperture (hereinafter, referred to as “CA”).
The third method is to perform convolution on an image which is in-focus in a single uniform way in a depth direction, by moving a focusing lens or an imaging device during exposure (that is synonymous with uniformity of blurs in the respective depths). In the method, the image restoration processing is performed on the obtained image, using a previously measured blur pattern or a blur pattern calculated by simulation, thereby producing the EDOF image. The method is called as flexible DOF (hereinafter, referred to as “F-DOF”) (see Patent Literature 1, for example).
Among the three methods, the third one, i.e., F-DOF, is the method by which most favorable image quality can be obtained, and which yields a superior EDOF effect. In addition, the F-DOF has an off-axis property which depends on a lens property itself, thereby easily enhancing capability. However, an optical condition requires a single subject be convoluted on a single image position, even if a focal position is moved during exposure. Accordingly, an image-space telecentric lens is required to be used.
The aforementioned EDOF has been applied to a microscope use for the longest time.
The EDOF has also been applied recently to a camera installed in a mobile phone and so on. The EDOF is used for the camera, enabling the camera to be miniaturized. This is because that the EDOF is effective to obtain a completely in-focus image (an image in which all subjects are in-focus) without an automatic focusing mechanism.
The EDOF can be further applied to a usual digital still camera and digital video camera. As a recent trend in the digital still camera and the digital video camera, these cameras are required to enable a user to perform shooting more easily with less failure. The EDOF can be expected to bring an effect of the completely in-focus image, i.e., release from making a mistake in focusing. For equipment to which the EDOF is applied, the most excellent method among the aforementioned methods is F-DOF because of it's high-quality image, significant EDOF effect, possibility of arbitrary change in a focal range, feasibility by applying the usual automatic focusing mechanism (unnecessity of a special optical system), and ease in switching between EDOF shooting and usual shooting.